The Prevalence of PMM2-CDG in Estonia Based on Population Carrier Frequencies and Diagnosed Patients.

PMM2-CDG (MIM#212065) is the most common type of congenital disorders of glycosylation (CDG) caused by mutations in PMM2 (MIM#601785). In Estonia, five patients from three families have been diagnosed with PMM2-CDG. Our aim was to evaluate the presence of different PMM2-CDG-causing mutations in a population-based cohort and to calculate the expected frequency of PMM2-CDG in Estonia. Also, we analyzed the prevalence of PMM2-CDG based on our patient group data. To calculate the expected frequency of PMM2-CDG, we used the whole genome sequencing data of 2,244 participants from biobank of the Estonian Genome Center, University of Tartu. Nineteen individuals carried mutated PMM2 alleles and altogether, five different mutations were identified. The observed carrier frequency for all PMM2 disease-causing mutations was thus 1/118, and for the most frequent mutation p.R141H, 1/224. The expected frequency of the disease in Estonian population is 1/77,000. It is comparable to the current prevalence of PMM2-CDG for the less than 18 years age group, which is 1/79,000. In conclusion, the frequency of PMM2-CDG in Estonia is lower than in other European populations reported thus far. We demonstrate that biobank data can be useful for gaining new information about the epidemiology of the PMM2-CDG.